How to automatically adjust font size with jQuery_jquery

$.fn.fontfit = function(max) {
  var max_size = 18;
  if (typeof(max) == "undefined")
    max = max_size;
  $(this).wrapInner('<div id="fontfit"></div>');
  var dheight = $(this).height();
  var cheight = $("#fontfit").height();
  var fsize = (($(this).css("font-size")).slice(0,-2))*1;
  while(cheight<dheight && fsize<max) {
    fsize+=1;
    $(this).css("font-size",fsize+"px");
    cheight = $("#fontfit").height();
  }
  while(cheight>dheight || fsize>max) {
    fsize-=1;
    $(this).css("font-size",fsize+"px");
    cheight = $("#fontfit").height();
  }
  $("#fontfit").replaceWith($("#fontfit").html());
  return this;
}